Strange. Unfortunately without being there to look at it all I can really tell you is it did have one when it was new.

 

looking good , hope you sort out the problem

 

i'm going to see if i can find any diagrams from the mits dealer...we don't see any unaccounted for plugs in the front, nor does it appear there is an empty spot for a pre-cat sensor, but I am using aftermarket headers now...so maybe they never came with that.

I may just reflash the ECU and delete the table value for this mysterious front-cat sensor (least then I lose the engine light).

Other than that minor item, she runs a little rich occasionally...over-chokes herself and the revs, when at idle sort of bounce between 500 to 1200...but suddenly the thermostat opens up (we think), and she purrs nicely at a stable 1000 or so. I was out driving for about 2 hours and this happened once...a little strange, not sure what it could be??

Here are a few pics I took at my friend's place:

 

Well that front 02 sensor is what the engine uses to determine the air/fuel ratio. The 2nd one has nothing to do with engine operation but rather to tell whether the cat is doing its job efficiently. If it were me I would try to find what is going on as the front 02 is pretty important.

 

no idea man, there is one unaccounted for plug/wire which is right in front of the radiator off the same harness from the horns...which is probably for the airbag.

no plugin for an o2 sensor on the headers and no wire hanging around there that isn't already plugged in.

i remember my 4G94 had the o2 sensor right on the headers but the 4G69 is different...i don't even know if it has one.......

 

Hopefully you can find what happened to it lol. I found a couple pics that show the front 02 sensor in roughly the same location as 4G94. Slighlty lower and towards the drivers side, might not be in the manifold it may be actually right at the start of the downpipe I cant find a pic showing the whole sensor. You sure the wire was not cut off right where it branches off the main harness and taped over?.

Edit:

After looking through the FSM the 4G69 shows both 02 sensors right next to the cat. One directly in front of the cat and the other directly behind it. Did you happen to miss a plug somewhere under the car where the other one is?

 

Hmm we didn't notice anything, I'll see what we can find next time I take it to the shop. Could not having this plugged in cause surging, for example in 3rd gear? Getting a little bit of that now...

Thanks for the help

 

This could cause any number of issues which is why I would take care of it first, otherwise you could end up chasing your tail trying to track down engine issues that could be caused from that missing 02.

 

Are you running the cat? or is it straight? If not cat you could try to use the rear 02 as the front input, not sure how you would change that in the rom though.

 

no cat, i bought the small weld-on cat from RRM if i run into any problems with the police...but i dont think i will, and i plan to turbo at some point which will quiet it down a lot

i'll see if i can take a few pictures of my header/downpipe setup from underneath, but even if there is an unaccounted for empty input, there sure as hell are no wires to read the o2 information...

 

took the car in. there simply is no wire for the front o2 sensor, nor is there an empty plug anywhere on the headers, or the downpipe.

the car is running very rich, burning fuel pretty fast, so this needs to be figured out but im at a loss as to how we can get the information to the computer from this ghost o2 sensor.

 

That is definitely due to that MIA o2 sensor but without a physical wire to get the info idk man that is a head scratcher

 

need RA guys to chime in here, help me locate this, because i do remember the o2 sensor being in plain sight on top of the headers when the 4G94 was in there, but even when i first got the 4G69 motor with its stock headers, i didn't see anywhere to plug an o2 sensor in (pre cat)

 

we managed to find what looks like the plug going to the ECU for front o2 sensor (4pin, orange, looks to be the same plug as the rear one we found)...it's tucked up near the right headlight harness/plugs...will need a fairly long o2 sensor cable to reach the downpipe, so i figure this plug that is missing from the RRM header/downpipes for the front o2 sensor should be closer to the headers (where heat is at its hottest anyway..) see picture:



computer is reading as only having an error now for the front o2 sensor, we think the rear one with the cat CEL eliminator is working..

seeing as there is no plug for a front o2 sensor, can i drill into, and weld on the headers/downpipe from RRM??

the car is running very rich, bit of black smoke occasionally even, we suspect this missing front o2 sensor is the culprit.

 

Yup you can drill into the pipe and weld in another bung for your front o2 sensor and get that connected. If you are still going to have to extend the o2 harness make sure you do it from the vehicle side of the wiring. DO NOT cut the wire harness from the o2 sensor itself as it should be shielded wires and any change in length will completely change the resistance causing issues (not to mention I don't think you can splice shielded wires anyways)